1. Field of the Invention
The present invention relates generally to a method of and a device for transporting a multi-phase fluid in conduits and pipes, such as mixtures of natural gas, water, and oil; geothermal and other mixtures of hot liquid and vapor; various pulps and slurries and the like.
2. Description of the Prior Art
It is known to transport multi-phase fluids in conduits or pipes. For the purposes of this specification, the terms "pipe" and "conduit" are used interchangeably. Pipes are known to have a variety of shapes, most commonly a circular shape. However, pipes of non-circular shapes, for example rectangular or square pipes can also be considered. The fluid mixture typically contains two or more individual phases. Each phase may consist of a gas, a liquid, or a number of solid particles. Although the phases do not usually interact with each other chemically, they effect each other hydraulically. The structure of the resultant steady state flow depends on the properties of the individual phases such as the fluid density and viscosity as well as on the flow conditions such as the pressure, temperature, in addition to the shape, orientation, inclination, and size of the conduit.
The phenomenon of a multi-phase flow is observed in many industries. A two-phase flow of a gas and a liquid is recognized in oil-gas pipelines and wells, air-lift pumps, oil refineries, steam boilers, electric power plants, geothermal wells, fluid carrying conduits operating in a zero gravity environment, and other fluid transportation and industrial processing facilities. A two-phase flow of a liquid and solids is known in various pulp and slurry conduits such as in paper processing equipment or transporting of coal, minerals, and the like. Interfacial mass transfer between the phases in a multi-phase flow is also utilized in chemical processing plants and reactors such as gas-fluid contacting reactors, water oxygenation and other liquid gasification devices.
In many cases, the mechanical properties of individual phases, primarily density, are distinctly different. That leads to substantial differences in the flow velocities of each phase. The phase with lower density usually occupies the central part of the conduit and moves faster than the phase with higher density. In a gas-liquid flow conduit, for example in a natural gas/oil well or pipeline, geothermal well, air-lift pump, fluid carrying conduit in zero gravity environment, and the like, the gas phase moves faster than the liquid phase. In addition, due to its less mass and momentum, the gas phase can change speed more rapidly than the liquid phase. This difference in dynamic behavior between the gas and a liquid phase creates unique flow conditions which are different than a single-phase gas or a single-phase liquid flow.
In a vertical or inclined large diameter pipe, as the percentage of gas phase in an upward gas-liquid flow increases, the gas phase speed becomes increasingly higher than the liquid phase speed. In an application where the potential energy of gas phase is used to transport the liquid phase, such as in an oil or geothermal well or in an air-lift pump, the efficiency of liquid delivery may be compromised. An example of such device is described in a U.S. Pat. No. 4,135,364 by Busick. The air-lift pump has a plurality of vertical lift tubes immersed in water and arranged to discharge water into a hood at their upper ends. Compressed air is introduced continuously or periodically into the lower part of each tube to form a bubble which pushes the water up the lift tube. Although capable of pumping water, this device has no provisions that would reduce the tendency of air to slip past the liquid and to collect in the center of the lift tube and flow faster then the water. There is a need, therefore, for a device with improved liquid delivery efficiency due to reduction in slippage between the phases in a multi-phase flow.
Similarly, in a horizontal or inclined large diameter pipe, the existence of a material percentage of a phase with lower density, such as gas, may lead to gas concentrations in a higher portions of the pipe which leaves the heavier density phase collecting at the lower portions of the pipe. As it collects in the lower parts of the piping system, the heavier phase liquid may form blockages and cause additional resistance to the overall flow. U.S. Pat. No. 4,972,804 by Stolmar describes quite an elaborate device to prevent the formation of stagnant volumes and associated with them sludge deposits in a steam generator. Typically, increasing pressure pushes the volumes of the heavier phase liquid out of the lower parts of the pipe thus relieving the pressure buildup. During these cycles of pressure buildups, the spikes in pressure may cause damage to the pipe and require the use of higher powered pumps and pipes with additional structural strength for such applications. Uneven flow may also cause processing difficulties at the receiving end of the pipe system. The need exists therefore for a conduit with continuous constant flow of all phases in a multi-phase flow environment which would prevent the formation of stagnant volumes of the heavier phase.
A turn in a pipe will decrease the speed of the relatively heavier phase of a multi-phase flow due to its higher density and inertia in comparison to the lighter phase. Especially in pipes with little interaction between the phases, this velocity reducing effect occurring in each turn in a pipe may have cumulative effect. As a result, each turn has an effect of changing the downstream flow mixture to the one with higher percentage of the lighter phase. The need exists therefore for a device that would reduce or eliminate this harmful effect.
In a slurry processing facility such as paper pulp plant, it is common to conduct a chemical treatment of a slurry by injecting gas such as chlorine in the mix of liquid and solids. Resultant three-phase flow is carried by conduits to the subsequent stages of processing. Separation and relative changes in individual phase speeds cause production problems not only due to uneven pulp supply but also due to pressure fluctuations. These pressure fluctuations require separate damping devices such as the one described in U.S. Pat. No. 4,179,332 by Ilmoniemi. There is, therefore, a need for a conduit which would ensure consistent flow of all phases as well as prevent pressure build-ups.
In a chemical industry, many chemical and evaporation process operations involve molecular mass transfer between the gas phase and a liquid phase across the gas-liquid interface. It is usually achieved by injection of gas into fluid stream. U.S. Pat. No. 5,666,811 by Grisham describes such an injector device. However, the objective of creating a substantial contact area between the phases is achieved only in vicinity of the injector port. Flow past the injector may separate again into two distinct phases without desirable interfacial contact. The need exist therefore for a conduit which would promote controlled substantial interfacial contact between the phases throughout the interactive or transporting stage in the manufacturing process.
In the electric power generation industry, steam turbines are often used. Usually, to increase the total pressure drop across the system, the steam is condensed at the exit of the turbine to create a low pressure area. In condensing the steam to water, energy of the system is rejected, or wasted, in the form of heat energy of the system plus the energy required to change the phase from steam to water, or the latent heat energy. This rejection of latent heat energy accounts for over 25% of system efficiency losses. The need exists therefore for a device which improves the efficiency of steam turbines by reducing these efficiency losses due to the inability to recover latent heat energy. This situation is also encountered in waste steam recovery operations commonly referred to as cogeneration facilities.